Researchers from Korea University, Seoul National University, University of New South Wales, University of Toledo, Chonnam National University, Ulsan National Institute of Science and Technology, Cardiff University and the University of Surrey have reported a new strategy to enhance both the efficiency and stability of perovskite solar cells by leveraging a previously unrecognized interfacial phenomenon termed contact-triggered cationic interaction (CCI).
A schematic of CCI between framework-embedded molecules of 3D and 2D perovskites. Image from: Nature Energy
Unlike conventional approaches based on additive incorporation or surface passivation, CCI arises from simple physical contact between separately crystallized two-dimensional (2D) and three-dimensional (3D) perovskite films, without chemical bonding, intermixing or junction formation. At the interface, bulky spacer cations in the 2D perovskite deform and interact with formamidinium (FA) cations in the 3D lattice via dipole-induced dipole interactions. These interactions constrain the rotational freedom of the FA cations, effectively reducing molecular disorder. The strength of this interaction increases with alkyl chain length in the 2D layer, which provides more contact points and further restricts cation motion. As a result, CCI suppresses phase transitions, extends carrier lifetimes, and modifies photophysical behavior in a reversible manner.
A key outcome of this process is a unique CCI-induced recrystallization of the 3D FAPbI3 lattice upon subsequent heating. This leads to the formation of a stable tetragonal phase with improved cation homogeneity, reduced lattice disorder, and crystal orientation more closely aligned with theoretical values. Importantly, this transformation occurs without incorporating 2D material into the bulk or forming permanent bilayers.
These structural improvements translate directly into enhanced optoelectronic properties. The treated films exhibit a photoluminescence quantum efficiency (PLQE) exceeding 50%, along with increased carrier mobility and lifetime. Experimentally, carrier lifetimes increased from 4.48 μs in untreated films to 5.89 μs following CCI treatment, indicating reduced non-radiative recombination losses.
Device performance reflects these material gains. Solar cells based on CCI-engineered FAPbI3 achieve a power conversion efficiency of 26.25%, with a certified value of 25.61% verified by the Solar Energy Research Institute of Singapore. In stability tests, the devices retained 95.2% of their initial efficiency after 2,000 hours of operation and demonstrated a projected operational lifetime of approximately 24,800 hours (exceeding 20,000 hours more generally reported).
Thermal robustness is also improved: under accelerated ageing conditions, the CCI-treated material requires roughly twice the thermal energy to degrade compared to comparable perovskites reported in recent literature.
Nanoscale characterization using photo-induced force microscopy (PiFM) confirmed that the interaction induces uniform molecular alignment throughout the film thickness, not just at the interface. This provides direct experimental validation that simple contact can reorganize the perovskite lattice at the molecular level across the bulk.
As noted by University of Surrey's Jae Sung Yun: "Perovskite solar cells could genuinely change how we generate electricity – they are cheaper to make than silicon panels and the efficiency numbers are now very competitive. The stumbling block has always been durability. What I find exciting about this work is how elegantly simple the solution turns out to be. You place two films in contact, and that contact alone reorganizes the material at a molecular level confirmed by our state-of-the-art nanoscale chemical imaging techniques – all the way through, not just at the surface. No extra chemicals, no added complexity. ”
This work provides the first quantitative evidence that intrinsic interfacial cationic interactions - activated purely by contact - can govern lattice structure, suppress phase instability, and significantly enhance both efficiency and long-term stability. The findings establish a new framework for molecular-level interface engineering in halide perovskites, where controlled contact, rather than chemical modification, defines material performance.
